The Wallace Line
There were actually two 'Wallace Lines'. Wallace originally placed his boundary
to the northwest of Sulawesi (Celebes), but later relocated it to the southeast
of this island. Without knowing it, Wallace had moved his line to a new
position that accurately matches the plate tectonic history of the archipelago.
The Australia and Eurasia plates collided fifteen million years ago, bringing
two communities into contact that had been isolated from one another since
the close of the Cretaceous (65 million years ago). During glacial maxima,
Sulawesi was in contact with the Eurasian mainland, while a deep ocean trench
separated Sulawesi from islands immediately to the southwest that were connected
to Australia and New Guinea. After Wallace, researchers drew a number of
other `lines' in this area - depending upon which animal group they studied.
Wallace used birds (especially parrots) but the dividing 'line' shifts across
the archipelago depending upon whether the subject studied was birds, mammals
or freshwater fish. At present, biologists recognize that there is a transition
zone between the Eurasian and Australian communities. This biogeographic
sub-region is known as Wallacia, in recognition of Wallace's pioneering
work.
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After Van Oosterzee
1997
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